In typical automotive windshield wiper systems of the type having a reciprocating drive link between a wiper arm and a motor driven crank arm, the wiper arm moves a blade through an arcuate wipe pattern between fixed inner and outer positions as the crank arm rotates continuously in one direction. According to numerous prior proposals, the wiper blade may be moved to a park position below the wipe pattern by increasing the length, or throw, of the crank arm during the final stroke of the wiper blade. In so called reverse-to-park depressed systems, the extra angular movement of the wiper blade beyond the inner wipe position is produced by a mechanism in the wiper drive system which automatically increases the length of the crank arm in response to the onset of reverse rotation of the wiper drive shaft.
In several such systems, an eccentric drive is arranged within the crank arm between the drive motor and the drive link. The crank arm maintains a folded or drive position when the motor shaft rotates in a first direction resulting in normal wiping of the windshield. When the direction of drive shaft rotation is reversed to a second direction of rotation, the eccentric drive automatically extends the crank arm to a park position. A crank arm, according to this invention, represents an improved variable length crank arm employing an eccentric drive.